Activated vitamins D.sub.3 including 1.alpha., 25-dihydroxy-vitamin D.sub.3 are known to have many physiological activities such as calcium catabolism regulation, growth inhibition and differentiation induction of tumor cells, immunoregulation. However, some activated vitamins D.sub.3 disadvantageously cause hypercalcemia during long-term and continuous administration so that they are not suitable for use as antitumor agents, antirheumatic agents or the like. Thus, a number of vitamin D derivatives have been synthesized and examined for the purpose of separating activities of these vitamins D.
For example, JPA No. 267550/86 discloses 1.alpha.,3.beta.-dihydroxy-20(S)-(3-hydroxy-3-methylbutyloxy)-9,10-secopre gna-5,7,10(19)-triene and JPA No. 330714/95 discloses a vitamin D derivative substituted by a sulfur atom at the 22-position.
Various vitamin D derivatives having a double bond at the 16-position are described in JPA No. 9861/90, JPA No. 17019/91, JPA No. 188159/95, JPA No. 40975/94, JPA No. 179418/95, U.S. Pat. No. 5,087,619 and U.S. Pat. No. 5,145,846, etc. However, none of these compounds are said to have weak hypercalcemic activity.
Many of these known vitamin D compounds have high binding ability to vitamin D receptors but strong hypercalcemic activity, or weak hypercalcemic activity but unsatisfactory binding ability to vitamin D receptors. Therefore, it would be desirable to develop promising compounds with high binding ability to vitamin D receptors and weak hypercalcemic activity.